This invention relates to a method and an apparatus for hydrolysis treatment of cellulosic fiber material.
In conventional systems, wood chips (or other cellulosic or fiber material) undergo hydrolysis in a first reactor vessel prior to introduction to a second vessel, e.g., a digester. One such conventional system is described in U.S. Pat. No. 4,174,997 ('997 patent). In the first reactor vessel, hydrolysis of the slurry of wood chips passing through that vessel occurs under acidic conditions. In the first reactor vessel, hydrolysate, e.g., sugars such pentose and hexose, is extracted from wood chips and the hydrolysate is recovered. Fiber material is discharged from the bottom of the first reactor vessel and transferred via the transfer line to the top of the second reactor vessel, e.g., digester, for cooking treatment of the cellulosic material.
In conventional systems, such as described in the '997 patent, hydrolysis occurs throughout the first reactor vessel. A chip slurry is introduced into the top of the first reactor vessel and is discharged from the bottom of the vessel. Heat is added to the vessel by introducing hot water, e.g., 150° C. degrees Celsius (° C.), to the bottom of the vessel and steam at the top of the vessel. In addition, acidic solutions were added to promote hydrolysis, especially where the material was at temperatures below 150° C. The hot water flows upward in the vessel, which is counter to the downward flow of fiber material. The hot water and steam provide sufficient heat to the material to maintain hydrolysis through the vessel.
In some conventional systems, cooking chemical such as white liquor is introduced to the bottom of the first reactor vessel and into a transfer pipe for transporting the chip slurry from the first reactor vessel to the second reactor vessel. The injection of cooking chemicals to the bottom of the first reactor vessel starts the impregnation of the fibers of the cellulosic material in the bottom of the first reactor vessel while the hydrolysis reaction is still underway. It is undesirable to introduce cooking chemicals to the cellulosic material while hydrolysis is ongoing.